This invention relates to organic polymeric gel-like materials chemically crosslinked and containing covalently bonded phosphoric acid molecules or a derivative thereof, which gels are acidic in character and capable of dissociation to the first or second degree. The materials are possessed of ion exchange properties, catalytic effects and the like. The polymers of the invention are preferably prepared by suspension copolymerization of acrylic or methacrylic acid derivatives containing one or more hydroxyl or epoxide groups with crosslinking comonomers containing two or more double bonds able to copolymerize therewith (for instance, acryloyl or methacryloyl double bonds, or with divinylbenzene or divinylsulfone), and by the subsequent reaction of the produced three-dimensional polymers containing free hydroxyl groups or epoxide groups with phosphoric acid or a derivative thereof. Besides the aforementioned crosslinked gels which are homogeneous, heterogeneous gels may also be prepared using established reaction conditions. The gels are notable for their permanent porosity even in a dry state, their well-defined pore size distribution and their large inner surfaces. These properties give the gel materials a satisfactory exchange capacity for the functional groups bonded at the surface thereof. The materials prepared in this way may be advantageously used as strong cation-exchangers, as efficient catalysts for chemical reactions, and also as polymer reactants employing the reactivity of the chemically bonded phosphoric acid or its halogen derivatives.
A large number of ion-exchangers are known which have strongly acidic functional groups bonded to organic polymers. Copolymers of styrene and divinylbenzene are predominantly used as carriers and sulfonic groups -SO.sub.3 H as the functional exchange groups. The styrene-divinylbenzene copolymers are mostly homogeneous and are noted for their three-dimensional structure having a low density of crosslinks, such that they will swell in certain solvents. The macroporous structure thereof is achieved by copolymerization with a higher amount of a crosslinking agent in the presence of inert solvents having various solvation powers relative to the polymer.
According to the present invention, strongly acidic cation-exchangers can be obtained by the chemical fixation of phosphoric acid molecules to a copolymeric matrix by the chemical reaction of the previously prepared polymeric gel with phosphoric acid or its derivative. The invention takes advantage of the ability of phosphoric acid or a derivative thereof to react with hydroxyl or epoxide groups present in the gel. The macroporous gels thus obtained have significant advantage, in many applications, since they exhibit a measurable constant porosity coupled with a large surface area at the point where the bonding reaction takes place. These properties afford easy accessibility of the acidic functional group for further reacting components. It should be noted that the characteristics do not, however, exclude the application of the aforementioned homogeneous crosslinked gels, modified by phosphorylation in accordance with the present invention, in some processes in the low-molecular-weight region, as in ion exchange, acid catalysis of organic reactions, and the like.
It is accordingly an object of the instant invention to avoid one or more drawbacks of the prior art.
It is a further object of the invention to provide for improved three-dimensional polymeric gel materials containing phosphoric acid residues capable of dissociation and a method for their preparation.
These and other objects of the invention will become more apparent from the following detailed disclosure and from the appended claims.